So yesterday, we had our first match and the question arised, if Veers can use his abilities like sharpshooter for the Maximum Firepower attack, and if he can convert surge to crit. The same goes for Leias Bombardement I guess.

Yes.

Its a shooting attack - effectively a weapon... The keywords that apply to his weapon (but are not part of his weapon) will apply.

To say it another way...

Unit card abilities and keywords apply to all weapons that unit uses. Keywords attached to a weapon are not applied to other weapons (unless combined in a dice pool).

Thx for the answer, thats how we played it^^